In multi-cylinder internal combustion engines, exhaust manifolds are typically in fluid communication with exhaust ports. In a typical in-line 6 cylinder engine, the exhaust manifold includes 6 ports connected to the exhaust ports and one exit passage connected to a turbo charger or exhaust pipe. For larger engines, the exhaust manifold may need to be greater than three feet in length. The heat differential and resulting thermal expansion experienced by a longer exhaust manifold generally prohibits a single piece manifold as the internal stresses and resulting stresses placed on the cylinder head connections exceed desired levels.
In a turbocharged application, generally the exhaust gasses are desirably routed from the cylinder head exhaust ports to the intake of the turbine with minimal loss of power. This requires that the exhaust gasses reach the turbine by following the shortest path. Multi-piece manifolds, therefore, have been developed for larger engines to route exhaust gasses to a turbocharger turbine, while allowing for thermal expansion of the exhaust manifold. Typically, a multi-piece exhaust manifold includes one or more connections that allow for relative movement of the connecting portions of the exhaust manifold sub-assembly portions.
In order to adequately seal between the exhaust manifold sub-assembly portions, the end connections are typically annular in form with one end of one sub-assembly interposed within another end of another sub-assembly, and the axis of each end generally aligned with the length of the exhaust manifold such that thermal expansion of the exhaust manifold sub-assemblies will result in relative axial movement between the ends. A ring seal can then be disposed between the ends to provide a seal that allows for the relative axial movement.
For lower heat applications, many polymers may be used to seal between the ends of the multi-piece exhaust manifold. With the advent of engines with higher operational temperatures to increase efficiency, polymers have been found to be undesirable and unable to provide the required sealing properties and material properties. Indeed polymers have been found to degrade with increase in temperature.
Referring to FIG. 1, a partial view of a prior art manifold 20 is illustrated. Manifold 20 includes a first portion 22 and a second portion 24. First portion 22 includes a generally hollow body 30 defining an annular connection end 32. Annular end connection 32 is defined in part by a cylindrical sealing surface 36. Second portion 24 includes a generally hollow body 40 defining an annular connection end 42. Annular end connection 42 is defined in part by a cylindrical sealing surface 46 that may be separated into three grooves 48. Each groove 48 accommodates a split ring (not shown) which is similar to a piston ring. Typically, the split rings are made of precisely machined Inconel™ alloy to provide a tight fit between the split rings and cylindrical sealing surfaces 36, 38.
When installed, both first portion 22 and second portion 24 are connected to a cylinder head (not shown) and are in fluid communication with at least one exhaust port of the cylinder head. Importantly, first portion 22 and second portion 24 are not in contact, with the split rings sealing therebetween and allowing for relative axial movement.
An advantage of the Inconel™ alloy split ring is that the material retains its desired sealing properties at increased operating temperatures. However, the split ring connection does not provide a positive seal as exhaust gasses may escape between the splits in the split rings. Another disadvantage of the split ring connection is that both the Inconel™ and the required machining are relatively costly. What is needed, therefore, is a seal between ends of a multi-piece exhaust manifold that provides a positive seal while reducing associated costs.